Steel Temperature Research Articles

Gradient Boosted Regression Trees for Modelling Onset of Austenite Decomposition During Cooling of Steels

Continuous cooling transformation (CCT) diagrams can be constructed by empirical methods, which is expensive and time consuming, or by fitting a model to available experimental data. Examples of data-driven models implemented so far include regression models, artificial neural networks, k-Nearest Neighbours and Random Forest. Gradient boosting machine (GBM) has been succesfully used in many machine learning applications, but has not been used before in modelling CCT-diagrams. This article presents a novel way of predicting ferrite start temperatures for low alloyed steels using gradient boosting. First, transformation onset temperatures are predicted over a grid of values with a trained GBM-model after which a physically-based model is fitted to the piecewise constant curve obtained as output from the model. Predictability of the GBM-model is tested with two sets of CCT-diagrams and compared to Random Forest and JMatPro software. GBM outperforms its competitors under all tested model performance metrics: e.g.R2 for test data is 0.92, 0.87 and 0.70 for GBM, Random Forest and JMatPro respectively. Output from the GBM-model is used for fitting a physically based model, which enables the estimation of transformation start for any linear or nonlinear cooling path. This can be further converted to Time-Temperature-Transformation (TTT) diagram.

Experimental investigation on galvanized steel elements at elevated temperature

Recent studies showed that hot galvanization can reduce the surface emissivity with abeneficial effect on the steel temperature. Therefore, background documents for next generation of Eurocode suggest considering this effect through a temperature dependant surface emissivity relationship. This paper shows the results of high-temperature small-scale tests, aimed at investigating the galvanization effect on steel plates temperature with variable section factors (A m/V). For each Am/V, both galvanized and blank steel specimens were tested to directly compare the temperatures, by using an input curve with a slower heating rate than ISO834 fire curve. The test results show that the heating in galvanized specimens was slower than the one recorded in blank samples, confirming the galvanization beneficial effect. To quantify this effect and to calibrate the emissivity of galvanized steel, the analytical method to assess steel temperature development, was applied using the temperature recorded in the furnace and in the samples. The surface emissivity was confirmed to be temperature dependant. Some applications of temperature dependant emissivity law were carried out, by varying Am/V and the fire curves, to quantify the galvanization beneficial effect. In particular, the ISO834 fire curve and several parametric fire curves, obtained by varying the opening factor, were considered.

A low bulk density, low thermal conductivity permanent lining castable for tundish obtained by adding pearlescent sand

AbstractThe precise control of molten steel temperature in tundish is a key factor to ensure the quality of the cast billets, so it is important to develop permanent lining castables for tundish with low thermal conductivity and bulk density. In this work, the hydrophobic modification of pearlescent sand was carried out with hydrogen silicone oil, and 3% of modified pearlescent sand was added to mullite‐bauxite castable to realize its low thermal conductivity and light weight. It is found that modified pearlescent sand still has good hydrophobicity at 350°C, the addition of modified pearlescent sand effectively increases the apparent porosity and reduces the bulk density of the castable. At 1500°C, the bulk density of modified pearlescent sand‐castable is 25.54% less than that of conventional castable. Compared with conventional castable, the mechanical properties and thermal shock resistance of modified pearlescent sand castable are worse, but they are sufficient to meet the use conditions of tundish permanent lining castable. At 600–1000°C, the thermal conductivity of the modified pearlescent sand castable is about 30% lower than that of the conventional castable, which proves that the addition of modified pearlescent sand can significantly improve the thermal insulation performance of mullite‐bauxite castable.

Machine-Learning-Based uncertainty and sensitivity analysis of Reinforced-Concrete slabs subjected to fire

Reinforced concrete (RC) slabs are integral parts of building structures and provide compartmentation functionality when subjected to fire. However, the fire resistance of RC slabs is affected by numerous factors that are mostly inherent uncertainties. Therefore, uncertainty and sensitivity analyses were conducted to examine the influence and significance of the potential uncertain parameters on the fire resistance of RC slabs. To this end, a set of RC slab samples with various design parameters were generated and different fire scenarios were considered using parametric fire curves. The slab samples were randomly coupled with the fire scenario samples. For each of the slab-fire pairs, finite-element simulations were conducted, and three specific fire durations were identified to represent the slab fire resistance corresponding to the failure criteria on the steel temperature (SP-Ⅰ), unexposed surface temperature (SP-Ⅱ), and mid-span deflection (SP- III). As a consequence, a database was established by collecting the calculated fire resistance for all the considered slab-fire samples. The prediction models of the slab fire resistance in association with uncertain parameters were developed by four commonly used ML algorithms, including linear regression, random forest, gradient boosting decision tree, and extreme gradient boosting. Among the developed ML-based prediction models, the extreme gradient boosting model was proven to have superior predictive accuracy. Therefore, it was further utilized for uncertainty analysis by considering 14 uncertain parameters from fire scenarios, material strengths, geometric dimensions, and external loads. The uncertainty analysis results showed that the considered uncertain parameters cause significant variability in the fire resistance of slabs, and the coefficients of variation were 11.5%, 13.1%, and 20.6% for the fire durations related to SP-Ⅰ, SP-Ⅱ, and SP- III, respectively. Moreover, the SHapley Additive exPlanations method was used to examine the sensitivity of the considered uncertain parameters. It was found that the parameters related to fire scenario were more influential to the fire resistance of slabs than the slab design parameters. The opening factor, slab thickness, and fire load density had noticeable effects on the fire resistance of SP-Ⅰ, SP-Ⅱ, and SP- III, respectively, whereas the uncertainties from material strengths and convection conditions had negligible effects.

Deformation behaviors at cryogenic temperature of lean duplex stainless steel with heterogeneous structure prepared by a short process

In this study, a lean duplex stainless steel with a heterogeneous lamellar structure is created using a quick technique of direct cold rolling combined with severe plastic deformation and short annealing. The deformation behaviors and fracture mechanisms at cryogenic temperature are investigated. In accordance with the findings, the duplex stainless steel S32304 exhibits excellent mechanical properties at 203 K, with tensile strength reaching 1160 MPa, elongation reaching 44.1%. Nearly 44.4% more elongation exists at 203 K than at 298 K. The synergistic coupling strengthening of the TRIP and TWIP effects of the austenite, HDI strengthening, and dislocation proliferation of coarse ferrite grains stimulated by the austenite grains with various orientations can all be credited for the excellent mechanical properties at 203 K. Additionally, the prominent deformation substructures, such as nanotwin bundles, and the strong interaction between dislocations and nanotwin bundles, are also contributed to strain hardening at 203 K. However, at 573 K, dislocation slip becomes the primary deformation mechanism of the two phases, and severe dislocation accumulations in the coarse ferrite grains become a possible site for crack nucleation, leading to a higher loss of ductility than at 298 K and 203 K.

Numerical simulation and correlation research of multi-track overlapping laser quenching process for 40Cr steel

Laser quenching has a short process cycle and high production efficiency, and it plays an important role in automobile, ship, machinery manufacturing, and other fields. The surface hardness of 40Cr steel laser quenching parts is uneven by unreasonable set on the quenching overlap zone. This will affect the microstructure of the quenched layer, resulting in cracking, corrosion during service, and other hazards that ultimately reduce reliability. Numerical simulations provide an effective way to quantitatively reveal the transient evolution of the multi-field coupling between temperature field, stress field, and phase transition field in quenching, which directly determines the extent of the overlap zone and quenching properties. The quenched phase transition layer profile is predicted to effectively determine the extent of the secondary tempering softening zone and solve the bottleneck problem of uneven surface hardness in quenching. The innovation of this paper is to establish a multi-field coupled numerical model of the 40Cr steel multi-track laser quenching process. The transient quenching temperature, phase transition hardening, and stress distribution were numerically calculated, and the size of the tempering zone under different overlapping rates was evaluated, revealing the internal coupling mechanism and correlation between multi-fields during the laser quenching. The quenching temperature, microstructure, and hardness distribution of 40Cr steel were tested by an infrared thermometer, Axio Vert A1 Zeiss microscope, Thermo ScientificTM Apreo scanning electron microscope, and Q10M microhardness tester, which verified the effectiveness of numerical simulation. The research can provide an important theoretical basis for optimizing quenching process parameters in production.

Dissimilar welding of austenitic SS and ferritic SS in last decades

Materials are very crucial and important factor in different industrial processes. Austenitic treated steel utilized overall in different significant businesses like synthetic, petrochemical, thermal energy station and vehicle dependent principally upon their corrosion opposition yet additionally for their formability, their solidarity, and their properties at outrageous temperatures. In any case, the expense of such steel is a significant worry to the ventures as the expense of austenitic treated steel is expanding step by step, because of the deficiency of its constituent Ni (Nickel). Thus, to keep away from this issue, the businesses could utilize a blend weld of two Steel having lower level of Ni. which would require right decision of filler material, welding method for an imperfection free sound weld. This paper endeavors an introductory survey of the most common way of joining significant contrasts among austenitic and ferritic Tempered Steel, its microstructure and corrosion opposition properties and mechanical properties in different Cycles and blends.

Energy demand in secondary steel making process: numerical analysis to assess the influence of the ladle working lining properties

In secondary steel making process, steel scrap is melted in an electric arc furnace, then poured into a ladle where ferroalloy are added to obtain the desired steel composition. Energy is also supplied in LF (Ladle Furnace) to guarantee steel temperature required in the teeming phase. In this paper a simplified, but sound numerical model of the process the ladle undergoes is presented: it is meant to provide a way to compare energy demand for different choices of materials used in the ladle or for changes in the ladle work cycle. As an example of application of the model, energy demand in LF are evaluated and compared for two different choices of the refractory material used as working lining: magnesia and alumina. To take into account the reduction of the working lining due to wear processes, energy demand has been calculated for three different thicknesses. In addition, the beneficial effect of a lid during the waiting phase after cleaning is investigated.

Effects of the microstructure and reversed austenite on the hydrogen embrittlement susceptibility of Ni-Cr-Mo-V/Nb high-strength steel

The effects of the microstructure and reversed austenite (RA) on the hydrogen embrittlement (HE) behavior were investigated in NiCrMoV/Nb high-strength steel prepared using three different heat treatments. The quenching and tempering (QT) steel showed a noble HE resistance for the lowest hydrogen diffusion and maximum apparent hydrogen concentration compared to quenching (Q) steel and quenching, lamellarizing, and tempering (QLT) steel. Thermal desorption spectroscopy (TDS) analysis confirmed that RA had an activation energy of 32.5 kJ/mol which indicates a stable trapping site. The QLT steel containing more RA exhibited a higher HE susceptibility, suggesting that RA degrades the HE resistance.

The role of austenite grain size on martensite start temperature and phase transformation path in SUS321 stainless steel

The change in Ms and transformation path of γ→α′ transformation with austenite grain size (AGS) has been investigated by a thermodynamic model of martensitic transformation and the stacking fault energy (SFE) in SUS321 stainless steel. With increasing AGS, the Ms increases and the SFE decreases. A good linear relationship is established between the Ms and the SFE. This result suggests that the martensitic transformation path changes as the AGS decreases, and the γ→ε→α′ sequence is gradually suppressed when the AGS is smaller than 3.5 μm.

Optimization of Coiling Temperature of Nb-Ti Containing High-Strength S700MC Grade Steel

Optimization of Coiling Temperature of Nb-Ti Containing High-Strength S700MC Grade Steel

Process model for manufacturing 400 series stainless steel with purified CO2 as an auxiliary oxidant and realizing carbon cycle

To reduce the CO2 emission in the iron and steel industry, aid carbon neutralization, and promote the application of CO2 in stainless steel production, CO and CO2 in flue gas were separated and purified to recycle for the production. Further, a process model of smelting stainless steel with O2–CO2 mixed injection was established based on the theory of thermodynamics and kinetics. The model validation was conducted in a 70 ton-stainless steel smelting furnace. The model calculation showed that CO2 injection for smelting stainless steel can improve the reaction efficiency of various elements in molten steel and cause a temperature drop. However, the excessive CO partial pressure in the molten pool caused by injecting CO2 aggravated the oxidation loss of chromium and led to a sharp rise in the temperature of molten steel near the end of smelting. According to the guidance of the model, a carbon cycle process concept was designed to realize the internal circulation application of CO2 in stainless steel production, which improves stainless steel smelting efficiency and self-consumption of CO2 produced by smelting.

Welding at Low Temperatures of Structural Steels

In this paper, the effect of direct and pulsed current in the arc welding with the use of UONI 13/Moroz coated electrodes on the structure and properties of 10KhSND structural low-alloy steel joints was investigated. Welding was performed in winter at an ambient temperature of-40oС. This work is a continuation of the cycle of research on welding of structural steels, carried out by the authors for several years.

Effect of magnetic disorder on Cr interaction with 1/2⟨111⟩ screw dislocations in bcc iron

We investigate how the magnetic state influences the interaction of Cr substitutional impurities with ½⟨111⟩ screw dislocations in bcc Fe via density functional theory (DFT). We compare the paramagnetic state, modeled with a non-collinear disordered local moment (DLM) model, with the ferromagnetic state. In a previous work [Casillas-Trujillo et al., Phys. Rev. B 102, 094420 (2020)], we have shown that the magnetic moment and atomic volume landscape around screw dislocations in the paramagnetic state of iron are substantially different from that in the ferromagnetic state. Such a difference can have an impact in the formation energies of substitutional impurities, in particular, magnetic solutes. We investigate the formation energies of Cr solutes as a function of position with respect to the screw dislocation core, the interaction of Cr atoms along the dislocation line, and the segregation profile of Cr with respect to the dislocation in paramagnetic and ferromagnetic bcc iron. Our results suggest that with increasing temperature and connected entropic effects, Cr atoms gradually increase their occupation of dislocation sites, close to twice the amount of Cr in the DLM case than in the ferromagnetic case, with possible relevance to understand mechanical properties at elevated temperatures in low-Cr ferritic steels in use as structural materials in nuclear energy applications.

Physical Simulation Study on Flow Field Characteristics of Molten Steel in 70t Ladle Bottom Argon Blowing Process

In the LF refining process, argon blowing at the bottom of ladle can play an important role in unifying the composition and temperature of molten steel and removing inclusions. However, unreasonable bottom argon blowing process can also cause many problems. Slag entrapment and slag surface exposure may occur, affecting the steel quality. Since the working conditions of different enterprises are very different, corresponding optimization is required for specific parameters. There were some problems in 70t ladle of a steel plant, such as unclear control of bottom argon blowing system in different refining periods, unobvious floating removal effect of inclusions in ladle, high total oxygen content and large fluctuation, etc. In this study, a 1:3 physical model was established according to the similarity principle. Then, on this basis, the experimental schemes with different blowing hole positions and argon flow rates were designed for simulation experiments. By means of mixing time measurement, flow field display and oil film measurement, the optimal argon blowing position was double holes 6, 12 (2/3R), and the included angle between them was 135°. The optimal argon flow rate for wire feeding and soft blowing should be 7.6 L/min (corresponding to the actual production of 180 L/min) and 0.6 L/min (corresponding to the actual production of 15 L/min), respectively. According to this scheme, the industrial experiments showed that the contents of total oxygen and nitrogen in the whole process were reduced, the surface density of inclusions in billet was reduced by 11.81% on average, and calcium sulfide and various inclusions containing aluminum were reduced to varying degrees.

Quantitative Analysis of Hardening Due to Carbon in Solid Solution in Martensitic Steels

The relationship between hardness and solute carbon concentration estimated via electrical resistivity measurement was investigated in as-quenched and tempered martensitic steels containing carbon of 0.3–0.6 mass%. As a result of corelating the amount of hardening due to carbon in solid solution with the solute carbon concentration, by the calculation to subtract precipitation strengthening, grain refinement strengthening, dislocation strengthening, and softening due to retained austenite from the total strengthening, we derived an equation of solid solution strengthening, where the hardening increases proportionally to the 1/2 or 2/3 power of the solute carbon concentration. It was confirmed that the effects of the factors other than solid solution strengthening due to carbon on hardness are relatively small in tempered specimens when the tempering temperature is less than 673 K; therefore, the change in hardness in tempered martensitic steels can be mostly explained by solute carbon concentration regardless of carbon content.

Experimental Study on Steel-Fiber-Reinforced Scoria Aggregate Concrete Subjected to Freeze-Thaw Cycles and Then Exposure to Elevated Temperatures

Steel-fiber-reinforced scoria aggregate concrete (SFSAC), which contains scoria aggregate and steel fiber, was developed to reduce the environmental impacts and improve the energy efficiency of buildings. Experimental studies were performed. The test variables included steel fiber volume contents (0%, 0.5%, 1.0%, and 1.5%), freeze-thaw cycles (0 and 25 times), and temperature (20 °C, 200 °C, 400 °C, 600 °C, and 800 °C). Mass loss, relative dynamic elastic modulus, mechanical properties, and the variation pattern of the complete stress–strain curves were analyzed through rapid freeze-thaw, high-temperature, and mechanical tests. The test results showed that after 25 freeze-thaw cycles and then exposure to high temperatures, the surfaces of SFSAC specimens showed aggregate spalling accompanied by dense cracks. Moreover, the residual mechanical properties of steel-fiber-reinforced natural aggregate concrete (SFNAC) were better than those of natural aggregate concrete (NAC). Although the incorporation of steel fiber cannot significantly improve the anti-freezing performance of SFSAC, it can improve the residual mechanical properties of SFSAC, and the optimal amount of incorporation is 1%, considering the economic cost factors. The stress–strain curves of both SFSAC and SFNAC showed the same trend after freeze-thaw cycles and then high temperatures, i.e., the peak stress decreased, the peak strain increased, and the descending section tended to level off. Finally, based on the concrete damage mechanics theory, considering the role of steel fibers in the uniaxial compression process of scoria aggregate concrete (SAC) and the effect of freeze-thaw and high-temperature tests on the SFSAC, the mechanical damage model and the uniaxial compression stress–strain constitutive model were proposed as being able to highly accurately reflect the overall process damage characteristics of SFSAC after freeze-thaw and then high-temperature tests, and also provided a theoretical basis for the high-temperature resistance assessment of SFSAC structures in cold regions.

Analysis of the Tensile Deformation Behaviors and Microstructure Characterization under Various Temperatures of MarBN Steel by EBSD

The uniaxial tensile behavior of MarBN steel with a constant strain rate of 5 × 10-5 s-1 under various temperatures ranging from room temperature to 630 °C was analyzed. This study aimed to identify the effect of the temperature on the tensile behavior and to understand the microstructure deformation by electron backscatter diffraction. The tensile results showed that the yield and ultimate tensile strength decreased with increasing temperature. Serrated flow was observed from 430 °C to 630 °C. The electron backscatter diffraction analysis showed that the low-angle grain boundaries decreased at the medium deformation and increased at the maximum deformation. In contrast, they decreased with increasing temperatures. In addition, the number of voids increased with the increasing plastic strain. As the strain increased, the voids joined together, and the tiny cracks became larger and failed. Three mechanisms were responsible for the tensile deformation failure at various temperatures: grain rotation, the formation and rearrangement of low angle grain boundaries, and void nucleation and propagation. Finally, the formation of the low-angle grain boundaries and voids under different degrees of deformation is discussed.

Influence analysis of alloy elements on irradiation embrittlement of RPV steel based on deep neural network

Reactor pressure vessel (RPV) is the most important core equipment in PWR. Its service life determines the service life of nuclear power plant and directly affects the economy and safety of nuclear power plant. Because RPV is serviced at high temperature, high pressure and high energy neutrons for a long time, the properties of RPV steel will significantly degrade, in which irradiation embrittlement is the most important factor for the structural integrity of RPV. In this work, about 700 groups of data such as composition, irradiation conditions and ductile brittle transition temperature of RPV steel are collected, and the data are cleaned and screened for modelling by machine learning. The deep neural network is used for establishing the correlation between key component and irradiation embrittlement of RPV steel. The results show that the lower flux of neutron irradiation will make the radiation embrittlement effect of RPV steel more obvious at the same neutron fluence. Cu, P and Ni are the key factors to influence the △DBTT of RPV steel. The synergistic effect of Cu and Ni on irradiation embrittlement is greater than that of Cu and Mn. These results will help to promote the optimization design of new RPV steel.

Effect of the Fire Modelling on the Structural Temperature Evolution Using Advanced Calculation Models

The main objective of this study is to compare the results in terms of gas temperature and structural elements temperature, using different localized fire models. In particular, with reference to an open car park fire, the simplified Hasemi localized fire model was firstly used for assessing the steel temperature of a typological steel-concrete beam. In the second step, the computational fluid dynamics (CFD) models were applied, also varying the geometry of the fire source; in the first case a 3D flame was considered, in the second case a flat flame source was modelled. The latter represented one of the main research novelties of this work. All the analyses were carried out without and with the activation of a sprinkler system, simulated by varying the Heat Release Rate curve, according to the Italian national fire technical code. The main results show that there was a significant effect of the fire model, indeed the Hasemi model generally overestimated the steel element temperature. Moreover, an effect of fire source modelling was observed, with greater temperature for a 3D fire source modelling in the case of no sprinkler activation. In all the analyses, to consider the sprinkler system leaded to a beneficial effect on temperature.